A centrifuge of the above-described general type has a rotor normally rotatable about an upright axis and carrying an array of pockets each formed as a sieve. These pockets have sieve forward faces, relative to the rotation direction, and are arrayed at angles to respective radii through the axis. Each pocket has a drain so that a solid/liquid mixture, such as sugar-beet or sugar-cane pulp, can be charged into the center of this rotor, whereupon it will be expelled radially outwardly. The pulp will be driven centrifugally against the inclined surfaces of these pockets to move slowly radially outwardly while the liquid phase of the suspension is drawn off as a primary or mother filtrate from the drains. Ideally such a sieve centrifuge should extract virtually all of the sugar from the pulp, leaving relatively dry and sugar-free pulp or bagasse at its solids-phase output.
In German Pat. No. 1,228,199 such a centrifuge is shown which is provided with a wash-liquid input that allows the solids/liquid mixture to be washed for leaching of all of the soluble components therefrom. Such an arrangement sprays the wash liquid directly on a relatively thin layer of the mixture being centrifuged, so that the leaching effect is often inadequate. In addition size factors make it impossible to subject the mixture to sufficient centrifugal force to extract most of the liquid phase, thereby leaving the solids relatively dry. What is more the wash liquid is inherently mixed with the primary filtrate, diluting it and making subsequent concentration of this primary filtrate substantially more difficult.
In German Pat. No. 1,119,775 another pocket-type centrifuge is shown which has the advantages of a large sieve area for a relatively small unit, and wherein the pockets are individually pivotal about respective vertical axes parallel to and offset from the rotation axis of the rotor. Such an arrangement does allow the centrifuge to be adjusted to efficiently process different types of solids/liquid mixtures, but has no provision whatsoever for using a wash liquid to completely leach out soluble substances from the mixture.
The arrangement of German Pat. No. 2,031,350 has a system wherein it is possible to extract virtually all of the liquid phase from the mixture. This arrangement uses a pair of concentric rotors to obtain extremely high centrifugal forces. As the material passes from the inner to outer rotor excellent extraction of the liquid phase is assured. Such an arrangement has, however, no provision for treating the mixture with a wash liquid, so that it is unsuitable for use in a sugar centrifuge.